help with helmets

Can anyone help me we are going to be getting a quest 88 dresden wheelchair bike for my 7 year old disabled daughter and i need to get her a helmet. The problem is that she has quite a wide head and a flat head at the back we have been to many local bike shops but with no success does anyone know of any specialist helmets or makers of bespoke helmets as we are running out of options. We may have to get a horse riding helmet made specially made which is going to cost me more than £500 . Can anyone HELP

My only concern is that most of the options for "special needs" are less than aesthetic, and also compromise the effectiveness as they are not cycle specific. Also if you have to "bodge" the fit ... it is proven that the use a poorly fitting helmet that can cause injuries

Secondly with my experience in riding recumbents, @summerdays is correct, helmets only really work with a "neck rest".

YOur choice of course as you know your daughter's skills and needs, but you will need to weigh up the need for a helmet in the first place if it compromises the ability to use the bike (if your daughter needs the head support)

How did the BMX ones fit? there is a brand or two that have an adjustment wheel at the back, as BMX helmets without that adjustment are difficult to get a good fit but most don't have that adjustment wheel. Sorry I can't remember the brand name though.